Percutaneous Tissue Excision Devices And Methods

ABSTRACT

A device for percutaneously excising tissue. In an embodiment, the device comprises an outer tubular. In addition, the device comprises an inner tubular slidingly received within the outer tubular, wherein the inner tubular has a distal end including an upper member and a lower member. Further, the device includes an open position with the distal end fully extended from the outer tubular, and a closed position with the distal end disposed within the outer tubular, wherein the upper member is biased away from the lower member and is disposed at an open angle θ O  relative to the lower member when the device is in the opened position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional application Ser. No.60/747,166 filed May 12, 2006, and entitled “Percutaneous TissueExcision Devices and Methods,” which is incorporated herein by referencein its entirety. This application also claims benefit of U.S.provisional application Ser. No. 60/704,224 filed Jul. 29, 2005, andentitled “Device for Resecting Spinal Tissue,” which is incorporatedherein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND

1. Field of the Invention

The present invention relates generally to minimally invasive methods,devices and systems for treating spinal disorders using imagingguidance. More particularly, the present invention relates to devicesand methods to reduce stenosis and increase the cross-sectional area ofthe spinal canal available for the spinal cord. Still more particularly,the present invention relates to devices and methods to percutaneouslyexcise portions of an enlarged ligamentum flavum.

2. Background of the Invention

The vertebral column (spine, spinal column, backbone) forms the mainpart of the axial skeleton, provides a strong yet flexible support forthe head and body, and protects the spinal cord disposed in thevertebral canal, which is formed within the vertebral column. Thevertebral column comprises a stack of vertebrae with an intervertebraldisc between adjacent vertebrae. The vertebrae are stabilized by musclesand ligaments that hold the vertebrae in place and limit the movementsof the vertebrae.

As illustrated in FIG. 1, each vertebra 10 includes a vertebral body 12that supports a vertebral arch 14. A median plane 210 generally dividesvertebra 10 into two substantially equal lateral sides. Vertical body 12has the general shape of a short cylinder and is anterior to thevertebral arch 14. The vertebral arch 14 together with vertebral body 12encloses a space termed the vertebral foramen 15. The succession ofvertebral foramen 15 in adjacent vertebrae 10 along the vertebral columndefine the vertebral canal (spinal canal), which contains the spinalcord.

Vertebral arch 14 is formed by two pedicles 24 which project posteriorlyto meet two laminae 16. The two laminae 16 meet posteriomedially to formthe spinous process 18. At the junction of pedicles 24 and laminae 16,six processes arise. Two transverse processes 20 projectposterolaterally, two superior articular processes 22 project generallysuperiorly and are positioned superior to two inferior articularprocesses 25 that generally project inferiorly.

The vertebral foramen 15 is generally an oval shaped space that containsand protects the spinal cord 28. Spinal cord 28 comprises a plurality ofnerves 34 surrounded by cerebrospinal fluid (CSF) and an outermostsheath/membrane called the dural sac 32. The CSF filled dural sac 32containing nerves 34 is relatively compressible. Posterior to the spinalcord 28 within vertebral foramen 15 is the ligamentum flavum 26 Laminae16 of adjacent vertebral arches 14 in the vertebral column are joined bythe relatively broad, elastic ligamentum flavum 26.

In degenerative conditions of the spine, narrowing of the spinal canal(stenosis) can occur. Lumbar spinal stenosis is often defined as a duralsac cross-sectional area less than 100 mm² or an anterior-posterior (AP)dimension of the canal of less than 10-12 mm for an average male.

The source of many cases of lumbar spinal stenosis is thickening of theligamentum flavum. Spinal stenosis may also be caused by subluxation,facet joint hypertrophy, osteophyte formation, underdevelopment ofspinal canal, spondylosis deformans, degenerative intervertebral discs,degenerative spondylolisthesis, degenerative arthritis, ossification ofthe vertebral accessory ligaments and the like. A less common cause ofspinal stenosis, which usually affects patients with morbid obesity orpatients on oral corticosteroids, is excess fat in the epidural spaceThe excessive epidural fat compresses the dural sac, nerve roots andblood vessels contained therein and resulting in back, leg pain andweakness and numbness of the legs. Spinal stenosis may also affect thecervical and, less commonly, the thoracic spine.

Patients suffering from spinal stenosis are typically first treated withexercise therapy, analgesics, and anti-inflammatory medications. Theseconservative treatment options frequently fail. If symptoms are severe,surgery is required to decompress the spinal cord and nerve roots.

In some conventional approaches to correct stenosis in the lumbarregion, an incision is made in the back and the muscles and supportingstructures are stripped away from the spine, exposing the posterioraspect of the vertebral column. The thickened ligamentum flavum is thenexposed by removal of a portion of the vertebral arch, often at thelaminae, covering the back of the spinal canal (laminectomy). Thethickened ligamentum flavum ligament can then be excised by sharpdissection with a scalpel or punching instruments such as a Kerisonpunch that is used to remove small chips of tissue. The procedure isperformed under general anesthesia. Patients are usually admitted to thehospital for approximately five to seven days depending on the age andoverall condition of the patient. Patients usually require between sixweeks and three months to recover from the procedure. Further, manypatients need extended therapy at a rehabilitation facility to regainenough mobility to live independently.

Much of the pain and disability after an open laminectomy results fromthe tearing and cutting of the back muscles, blood vessels, supportingligaments, and nerves that occurs during the exposure of the spinalcolumn. Also, because the spine stabilizing back muscles and ligamentsare stripped and detached from the spine during the laminectomy, thesepatients frequently develop spinal instability post-operatively.

Minimally invasive techniques offer the potential for lesspost-operative pain and faster recovery compared to traditional opensurgery. Percutaneous interventional spinal procedures can be performedwith local anesthesia, thereby sparing the patient the risks andrecovery time required with general anesthesia. In addition, there isless damage to the paraspinal muscles and ligaments with minimallyinvasive techniques, thereby reducing pain and preserving theseimportant stabilizing structures.

Various techniques for minimally invasive treatment of the spine areknown. Microdiscectomy is performed by making a small incision in theskin and deep tissues to create a portal to the spine. A microscope isthen used to aid in the dissection of the adjacent structures prior todisceetomy. The recovery for this procedure is much shorter thantraditional open discectomies. Percutaneous discectomy devices withfluoroscopic guidance have been used successfully to treat disorders ofthe disc but not to treat spinal stenosis or the ligamentum flavumdirectly. Arthroscopy or direct visualization of the spinal structuresusing a catheter or optical system have also been proposed to treatdisorders of the spine including spinal stenosis, however these devicesstill use miniaturized standard surgical instruments and directvisualization of the spine similar to open surgical procedures. Thesedevices and techniques are limited by the small size of the canal andthese operations are difficult to perform and master. In addition, theseprocedures are painful and often require general anesthesia. Further,the arthroscopy procedures are time consuming and the fiber opticsystems are expensive to purchase and maintain.

Still further, because the nerves of the spinal cord pass through thespinal canal directly adjacent to and anterior to the ligamentum flavum,any surgery, regardless of whether open or percutaneous, includes a riskof damage to the nerves of the spinal cord.

Hence, it remains desirable to provide simple methods, techniques, anddevices for treating spinal stenosis and other spinal disorders withoutrequiring open surgery. It is further desired to provide a systemwhereby the risk of damage to the dural sac containing the spinal nervesmay be reduced.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

These and other needs in the art are addressed in one embodiment by adevice for percutaneously excising tissue. In an embodiment, the devicecomprises an outer tubular member. In addition, the device comprises aninner tubular member slidingly received within the outer tubular member,wherein the inner tubular member has a distal end including an uppermember and a lower member. Further, the device includes an open positionwith the distal end fully extended from the outer tubular, and a closedposition with the distal end disposed within the outer tubular, whereinthe upper member is biased away from the lower member and is disposed atan open angle θ_(O) relative to the lower member when the device is inthe opened position.

These and other needs in the art are addressed in another embodiment bya method for treating stenosis in a spine of a patient having a medianplane, the spine including a spinal canal having a posterior surface, adural sac and an epidural space between the posterior surface and duralsac, the location of the stenosis determining a region of interest inthe spine. In an embodiment, the method comprises the step ofpositioning a tissue excision device adjacent the region of interest,wherein the tissue excision device comprises an outer tubular member andan inner tubular member slidably received within the outer tubularmember, wherein the inner tubular member has a distal end including anupper member and a lower member. In addition, the method comprises thestep of opening the tissue excision device by extending the distal endof the inner tubular from the outer tubular. Further, the methodcomprises the step of inserting the tissue excision device into tissuein the region of interest. Still further, the method comprises the stepof closing the tissue excision device by sliding the outer tubular overthe distal end of the inner tubular. Moreover, the method comprises thestep of retracting the tissue excision device from the tissue in theregion of interest.

These and other needs in the art are addressed in another embodiment bya a kit for performing a procedure on a spine, the spine including anepidural space containing a dural sac. In an embodiment, the kitcomprises an insertion member for accessing the epidural space. Inaddition, the kit comprises a volume of a contrast medium adapted to beinserted into the epidural space by the insertion member and expanded soas to compress a portion of the thecal sac and provide a safety zonewithin the epidural space. Further, the kit comprises a tissue excisiondevice comprising an outer tubular member and an inner tubular memberslidably received within the outer tubular member, wherein the innertubular member has a distal end including an upper member and a lowermember.

Thus, embodiments described herein comprise a combination of featuresand advantages intended to address various shortcomings associated withcertain prior devices. The various characteristics described above, aswell as other features, will be readily apparent to those skilled in theart upon reading the following detailed description of the preferredembodiments, and by referring to the accompanying drawings. It should beappreciated by those skilled in the art that the conception and thespecific embodiments disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the embodiments described herein. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference is made tothe accompanying drawings, wherein:

FIG. 1 is cross-section of the spine viewed from the space between twovertebrae, showing the upper surface of one vertebra and the spinalcanal with the dural sac and a normal (un-stenosed) ligamentum flavumtherein;

FIG. 2 is an illustration of the same section as FIG. 1, showing thespinal canal with the dural sac and a thickened ligamentum flavumtherein;

FIG. 3 is an enlarged cross-section of a vertebral foramen, showing asafety zone created by compression of the dural sac;

FIG. 4 is the cross-section of FIG. 3, showing a tissue excision toolpositioned in the ligamentum flavum according to a first method (ILAMP);

FIG. 5 is the cross-section of FIG. 3, showing a tissue excision toolpositioned in the ligamentum flavum according to an alternative method(MILD);

FIG. 6 is a partial cross-section of the lumbar portion of the vertebralcolumn taken along lines 6-6 in FIG. 1;

FIG. 7 is the cross-section of FIG. 6, showing the orientation of animaging tool relative to the vertebral column;

FIG. 8 is the cross-section of FIG. 6, showing the orientation of aninstrument relative to the vertebral column;

FIG. 9 is a perspective view of the distal portion of an embodiment of atissue excision device in an open position

FIG. 10 is a cross-sectional view of the tissue excision deviceillustrated in FIG. 9;

FIGS. 11-13 are series of side views of the tissue excision deviceillustrated in FIG. 9 transitioning from an open position to a closedposition;

FIGS. 14 and 15 are sequential illustrations showing the excision oftissue by the tissue excision tool illustrated in FIG. 9;

FIG. 16 is a perspective view of the distal portion of an embodiment ofanother tissue excision device in an open position;

FIG. 17 is a partial cut-away view of an embodiment of a tissue ejectiondevice; and

FIG. 18 is a schematic cross-section showing one embodiment of thepresent tool inserted into tissue via a cannula.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

For purposes of this discussion, the x-, y-, and z-axes are shown inFIGS. 1, 3, 5, 6, and 7 to aid in understanding the descriptions thatfollow The x-, y-, and z-axes have been assigned as follows. The x-axisis perpendicular to the longitudinal axis of the vertebral column andperpendicular to the coronal/frontal plane (i.e., x-axis definesanterior vs. posterior relationships). The y-axis runs substantiallyparallel to the vertebral column and perpendicular to the transverseplane (i.e., y-axis defines superior vs. inferior relationships). Thez-axis is perpendicular to the longitudinal axis of the vertebral columnand perpendicular to the median/midsagittal plane (i.e., z-axis definesthe lateral right and left sides of body parts). The set of coordinateaxes (x-, y-, and z-axes) are consistently maintained throughoutalthough different views of vertebrae and the spinal column may bepresented.

It is to be understood that the median/midsagittal plane passes from thetop to the bottom of the body and separates the left and the right sidesof the body, and the spine, into substantially equal halves (e.g., twosubstantially equal lateral sides). Further, it is to be understood thatthe frontal/coronal plane essentially separates the body into theforward (anterior) half and the back (posterior) half, and isperpendicular to the median plane. Still further, it is to be understoodthat the transverse plane is perpendicular to both the median plane andcoronal plane and is the plane which divides the body into an upper anda lower half.

The Spinal Canal and Spinal Stenosis

Referring again to FIG. 1, vertebral foramen 15 contains a portion ofthe ligamentum flavum 26, spinal cord 28, and an epidural space 27between ligamentum flavum 26 and spinal cord 28. Spinal cord 28comprises a plurality of nerves 34 surrounded by cerebrospinal fluid(CSF) contained within dural sac 32. Nerves 34 normally comprise only asmall proportion of the dural sac 32 volume. Thus, CSF filled dural sac32 is somewhat locally compressible, as localized pressure causes theCSF to flow to adjacent portions of the dural sac. Epidural space 27 istypically filled with blood vessels and fat. The posterior border of thenormal epidural space 27 generally defined by the ligamentum flavum 26,which is shown in its normal, non-thickened state in FIG. 1.

FIG. 2 illustrates a case of spinal stenosis resulting from a thickenedligamentum flavum 26 Since vertebral foramen 15 is defined andsurrounded by the relatively rigid bone its volume is essentiallyconstant Thus, thickening of ligamentum flavum 26 within vertebralforamen 15 can eventually result in compression of spinal cord 28. Inparticular, the thickened ligamentum flavum 26 may exert a compressiveforce on the posterior surface of dural sleeve 32. In addition,thickening of ligamentum flavum 26 may compress the blood vessels andfat occupying epidural space 27.

Compression of spinal cord 28, particularly in the lumbar region, mayresult in low back pain as well as pain or abnormal sensations in thelegs. Further, compression of the blood vessels in the epidural space 27that houses the nerves of the cauda equina may result in ischemic paintermed spinal claudication.

In order to relieve the symptoms associated with a thickened or enlargedligamentum flavum 26, methods, techniques, and devices described hereinmay be employed to reduce the compressive forces exerted by thethickened ligamentum flavum on spinal cord 28 and the blood vessels inepidural space 27 (e,g decompress spinal cord 28 and blood vessels inepidural space 27). In particular, compressive forces exerted by thethickened/enlarged ligamentum flavum 26 may be reduced by embodiments ofa minimally invasive ligament decompression (MILD) procedure describedherein. In some embodiments, the MILD procedure may be performedpercutaneously to reduce the size of ligamentum flavum 26 by excisingportions of ligamentum flavum 2. In particular, in some embodiments ofthe MILD procedure, the ligamentum flavum 26 is accessed, cut andremoved ipsilaterally (i.e., on the same side of vertebral arch 14) by apercutaneous cranial-caudal approach. Such an embodiment of the MILDprocedure may be described hereinafter as Ipsilateral Approach MILDProcedure (ILAMP).

Creation of a Safety Zone

As shown in FIGS. 1 and 2, ligamentum flavum 26 is posteriorly apposedto spinal cord 28. Thus, placement of tools within ligamentum flavum 26to excise portions of ligamentum flavum 26 creates a risk of forinadvertent damage to the spinal cord 28, dural sac 32, and/or nerves34. Thus, in preferred embodiments of the procedures described herein,prior to insertion of tissue excision devices into the ligamentum flavum26, a gap is advantageously created between ligamentum flavum 26 andspinal cord 28 to provide a safety zone between ligamentum flavum 26 andspinal cord 28.

FIG. 3 illustrates an enlarged cross-sectional view of a vertebralforamen 15 within a vertebra. Vertebral foramen 15 includes epiduralspace 27 and spinal cord 28 containing nerves 34 and CSF within duralsac 32. Further, a thickened/enlarged ligamentum flavum 26 extends intovertebral foramen 15. To reduce the risk of damage to dural sac 32 andspinal cord 28, a safety zone 40 is created between ligamentum flavum 26and dural sac 32.

As previously described, spinal cord 28 comprises nerves 34 surroundedby CSF and is contained within dural sac 32. Since more than 90% of thevolume of dural sac 32 in the lumbar region is filled by CSF, dural sac32 is highly compressible. Thus, even when stenosis is causingcompression of spinal cord 28, in most cases it is possible totemporarily compress spinal cord 28 further. Thus, according topreferred embodiments, dural sac 32 is further compressed in the regionof interest by injecting a fluid into epidural space 27 to create safetyzone 40. The fluid may be injected into the epidural space 27 with aninsertion member, such as a needle. The presence of the injected fluidcomprising safety zone 40 gently applies an additional compressive forceto the outer surface of dural sac 32 so that at least a portion of theCSF within dural sac 32 is forced out of dural sac 32 in the region ofinterest, resulting in safety zone 40 between dural sac 32 andligamentum flavum 26.

According to some embodiments, dural sac 32 is compressed by injecting astandard radio-opaque non-ionic myelographic contrast medium or otherimagable or non-imagable medium into epidural space 27 in the region ofinterest. This is preferably accomplished with a percutaneous injection.Sufficient injectable fluid is preferably injected to displace the CSFout of the region of interest and compress dural sac 32 to at least adesired degree. The injected medium is preferably substantiallycontained within the confines of epidural space 27 extending to themargins of the dural sac 32. The epidural space is substantiallywatertight and the fatty tissues and vascularization in epidural space27, combined with the viscous properties of the preferred fluids, serveto substantially maintain the injected medium in the desired region ofinterest. This novel method for protecting spinal cord 28 column may bereferred to hereinafter as “contrast-guided dural protection.”

Once a safety zone 40 has been created, a tissue excision tool or device100 may be inserted into the ligamentum flavum 26. Device 100 maycomprise any suitable device, tool or instrument for relieving stenosiscaused by the thickened/enlarged ligamentum flavum 26 including withoutlimitation, embodiments of tissue excision devices and tissue retractiondevices described in more detail below. Further, as best illustrated inFIG. 4, device 100 is inserted and positioned in the ligamentum flavum26 on the same side (ipsilateral) of median plane 210 as device 100percutaneously accesses the body, such that device 100 does not crossmedian plane 210. In another embodiment, as best illustrated in FIG. 4,device 100 is positioned in the ligamentum flavum 26 on the oppositeside of median plane 210 as device 100 percutaneously accesses the body,such that device 100 crosses median plane 210. In some embodiments,tissue excision device 100 may be guided by and advanced through acannula toward the ligamentum flavum 26. In other embodiments, a cannulais not be employed to guide device 100 as it is advanced towardligamentum flavum 26.

While it is preferred that the tip of device 100 remain withinligamentum flavum 26 as shown, the presence of safety zone 40 reducesthe likelihood that dural sac 32 will be damaged, even if the tip ofdevice 100 breaks through the anterior surface of ligamentum flavum 26.

Because the present techniques are preferably performed percutaneously,certain aspects of the present invention may be facilitated by imaging.Imaging windows (e.g., a fluoroscopic window of access—FWA) may beemployed to aid in performance of all or part of the proceduresdescribed herein. For instance, an imaging window may be employed to aidin insertion of device 100 into ligamentum flavum 26 as shown in FIG. 4.Preferable imaging windows/views are described in more detail below.

In this context, the spine can be imaged using any suitable technology,including without limitation, 2D fluoroscopy, 3D fluoroscopy, CT, MRI,ultrasound or with direct visualization with fiber optic ormicrosurgical techniques. Stereotactic or computerized image fusiontechniques are also suitable. Fluoroscopy is currently particularlywell-suited to the techniques disclosed herein. Fluoroscopic equipmentis safe and easy to use, readily available in most medical facilities,relatively inexpensive. In a typical procedure, using direct biplanefluoroscopic guidance and local anesthesia, epidural space 27 isaccessed for injection of contrast media adjacent to the surgical site.

If the injected medium is radio-opaque, as are for example myelographiccontrast media, the margins of expanded epidural space 27 will bereadily visible using fluoroscopy or CT imaging. Thus, safety zone 40created by the present contrast-guided dural compression techniques canreduce the risk of damage to dural sac 32 and spinal cord 28 during MILDprocedures to remove or displace portions of ligamentum flavum 26 and/orlaminae 16 in order to treat spinal stenosis.

Injectable Medium

If desired, the injected medium can be provided as a re-absorbablewater-soluble gel, so as to better localize safety zone 40 at the siteof surgery and reduce leakage of this protective layer from thevertebral/spinal canal. An injectable gel is a significant improvementon prior epidural injection techniques. The gel is preferablysubstantially more viscid than conventional contrast media and therelatively viscid and/or viscous gel preferably tends to remainlocalized at the desired site of treatment as it does not spread as muchas standard liquid contrast media that are used in epidurography. Thismay result in more uniform compression of dural sac 32 and less leakageof contrast out of the vertebral/spinal canal. In addition, preferredembodiments of the gel are re-absorbed more slowly than conventionalcontrast media, allowing for better visualization during the course ofthe surgical procedure.

In some embodiments, a contrast agent can be included in the gel itself,so that the entire gel mass is imagable. In other embodiments, an amountof contrast can be injected first, followed by the desired amount ofgel, or an amount of gel can be injected first, followed by the desiredamount of contrast. In this case, the contrast agent is captured on thesurface of the expanding gel mass, so that the periphery of the mass isimagable.

Any standard hydrophilic-lipophilic block copolymer (Pluronic) gel suchas are known in the art would be suitable and other gels may be used asthe injectable medium. The gel preferably has an inert base. In certainembodiments, the gel material is liquid at ambient temperatures and canbe injected through a small bore, such as a 27 gauge needle. The gelthen preferably becomes viscous when warmed to body temperature afterbeing injected. The viscosity of the gel can be adjusted through thespecifics of the preparation. The gel or other fluid is preferablysufficiently viscid or viscous at body temperature to compress andprotect dural sac 32 in the manner described above and to remainsufficiently present in the region of interest for at least about 30minutes. Thus, in some embodiments, the injected gel attains a viscositythat is two, three, six or even ten times that of the fluids that aretypically used for epidurograms.

In certain embodiments, the injected medium undergoes a reversiblechange in viscosity when warmed to body temperature so that it can beinjected as a low-viscosity fluid, thicken upon injection into thepatient, and be returned to its low-viscosity state by cooling. In theseembodiments, the injected medium is injected as desired and thickensupon warming, but can be removed by contacting it with a heat removaldevice, such as an aspirator that has been provided with a cooled tip.As a result of localized cooling, the gel reverts to its initial nonviscous liquid state and can be easily suctioned up the cooled needle orcatheter.

An example of a suitable contrast medium having the desired propertiesis Omnipaque® 240 available from Nycomed, N.Y., which is a commerciallyavailable non-ionic iodinated myelographic contrast medium. Othersuitable injectable media will be known to those skilled in the art.Because of the proximity to spinal cord 28 and spinal nerves 34, it ispreferred not to use ionic media in the injectable medium The preferredcompositions are reabsorbed relatively rapidly after the procedure. Thusany residual gel compression on dural sac 32 after the MILD proceduredissipates relatively quickly. For example, in preferred embodiments,the gel would have sufficient viscosity to compress dural sac 32 forthirty minutes, and sufficient degradability to be substantiallyreabsorbed within approximately two hours.

The injected contrast medium further may further include one or morebioactive agents. For example, medications such as those used inepidural steroid injection (e.g. Depo medrol, Celestone Soluspan) may beadded to the epidural gel to speed healing and reduce inflammation,scarring and adhesions. The gel preferably releases the steroidmedication slowly and prolongs the anti-inflammatory effect, which canbe extremely advantageous. Local anesthetic agents may also be added tothe gel. This prolongs the duration of action of local anesthetic agentsin the epidural space to prolong pain relief during epidural anesthesiaIn this embodiment the gel may be formulated to slow the reabsorption ofthe gel.

The present gels may also be used for epidural steroid injection andperineural blocks for management of acute and chronic spinal pain.Thrombin or other haemostatic agents can be added if desired, so as toreduce the risk of bleeding.

In some embodiments, the gel may also be used as a substitute for ablood patch if a CSF leak occurs. The gel may also be used as analternative method to treat lumbar puncture complications such aspost-lumbar puncture CSF leak or other causes of intracranialhypotension. Similarly, the gel may be used to patch postoperative CSFleaks or dural tears. If the dural sac were inadvertently torn or cut,then gel could immediately serve to seal the site and prevent leakage ofthe cerebral spinal fluid.

Ipsilateral Approach for MILD Procedure (ILAMP)

Once safety zone 40 has been created, the margins of epidural space 27are clearly demarcated by the injected medium and may be visualizedradiographically if an imageable medium has been used. As mentionedabove, percutaneous procedures can then more safely be performed onligamentum flavum 26 and/or surrounding tissues with reduced potentialfor injuring dural sac 32 and spinal cord 28.

A variety of suitable techniques and devices may be employed to reducethe size of the thickened/enlarged ligamentum flavum 26, therebydecompressing spinal cord 28 as well as blood vessels contained withinthe epidural space 27. Examples of suitable decompression techniquesinclude without limitation, removal of tissue from ligamentum flavum 26,laminectomy, laminotomy, and retraction and anchoring of ligamentumflavum 26. In some embodiments, all or a portion of ligamentum flavum 26is excised using a tissue excision device or tool (e.g., device 100).Embodiments of tissue excision tools are described in more detail below.

Accessing ligamentum flavum 26 with a tissue excision device 100 toremove portions of ligamentum flavum 26 can present significantchallenges. For instance, in some conventional approaches to correctstenosis caused by an enlarged ligamentum flavum, an incision is made inthe back of the patient and then the muscles and supporting structuresof the vertebral column (spine) are stripped away, exposing theposterior aspect of the vertebral column. Subsequently, the thickenedligamentum flavum is exposed by removal of a portion of vertebral arch14, often at lamina 16, which encloses the anterior portion of thespinal canal (laminectomy). The thickened ligamentum flavum ligament canthen be excised by sharp dissection with a scalpel or punchinginstruments. However, this approach is usually performed under generalanesthesia and typically requires an extended hospital stay, lengthyrecovery time and significant rehabilitation. Referring briefly to FIG.2, as another example, some MILD procedures access ligamentum flavum 26percutaneously by boring a hole through the vertebral arch 14 ofvertebra 10, often through a lamina 16. A cannula and/or device 100 maybe passed through the bore and/or anchored to the bore to accessligamentum flavum 26 for excision. However, while such a MILD approachis minimally invasive and reduces recovery time, such an approachrequires the additional step of boring a hole in the posterior of thevertebra 10 of interest. Thus, in some cases it will be preferable toemploy a MILD that percutaneously accesses ligamentum flavum 26 withoutthe need to cut or bore through the vertebrae.

FIG. 6 is a partial cross-sectional lateral view of a segment of avertebral column 80. The segment of vertebral column 80 illustrated inFIG. 5 includes three vertebrae 10 a, 10 b, and 10 c. Each vertebra 10a, 10 b, 10 c includes a vertebral body 12 a, 12 b, 12 c, that supportsa vertebral arch 14 a, 14 b, 14 c, respectively Vertical body 12 a, 12b, 12 c is anterior to vertebral arch 14 a, 14 b, 14 c, respectively.Each vertebral arch 14 a, 14 b, 14 c together with vertebral body 12 a,12 b, 12 c, respectively, encloses a vertebral foramen 15 a, 15 b, 15 c.The succession of vertebral foramen 15 a, 15 b, 15 c in adjacentvertebrae 10 a, 10 b, 10 c define vertebral canal 81 (spinal canal) thatruns along the length of vertebral column 80. Vertebral canal 81contains the spinal cord (not shown in FIG. 5).

As previously described, each vertebral arch 14 a, 14 b, 14 c includestwo pedicles 24 a, 24 b, 24 c, which project posteriorly to meet twolamina 16 a, 16 b, 16 c, respectively. It is to be understood that inthis view, one pedicle has been removed from each vertebra 10 a, 10 b,10 c and only the cross-section of one lamina 16 a, 16 b, 16 c isvisible. The two lamina 16 a, 16 b, 16 c meet posteriomedially to formthe spinous process 18 a, 18 b, 18 c, respectively.

Lamina 16 a, 16 b, 16 c of adjacent vertebra 10 a, 10 b, 10 c areconnected by ligamentum flavum 26 (shown in cross-section). Therelatively elastic ligamentum flavum 26 extends almost vertically fromsuperior lamina to inferior lamina of adjacent vertebrae. In particular,ligamentum flavum 26 originates on the inferior surface of the laminaeof the superior vertebrae and connects to the superior surface of thelaminae of the inferior vertebrae. For instance, ligamentum flavum 26originates on the inferior surface of lamina 16 a of superior vertebra10 a and connects to the superior surface of lamina 16 b of the inferiorvertebra 10 b. Thus, ligamentum flavum 26 spans an interlaminar space 82(i.e., space between laminae of adjacent vertebrae). Interlaminar space82 is generally the space between laminae of adjacent vertebrae inspinal column 80.

Still referring to FIG. 6, each lamina 16 a, 16 b, 16 c comprises arelatively broad flat plate of bone that extends posteromedially andslightly inferiorly from pedicles 24 a, 24 b, 24 c, respectively. Alongthe length of vertebral column 80, the lamina 16 a, 16 b, 16 c overlaplike roofing shingles, with each lamina substantially parallel to and atleast partially overlapping the adjacent inferior lamina. Further, theadjacent substantially parallel laminae are separated by the interveningligamentum flavum 26 and interlaminar space 82. For instance, lamina 16a is substantially parallel to and partially overlaps adjacent inferiorlamina 16 b and is separated from lamina 16 b by ligamentum flavum 26and interlaminar space 82.

FIG. 7 illustrates vertebral column 80 as it may be oriented with theanterior side positioned down and posterior back surface 85 positionedupward, as may be encountered during a spinal procedure or surgery. Inaddition, in the embodiment illustrated in FIG. 6, ligamentum flavum 26is thickened/enlarged, resulting in spinal stenosis In particular, theanterior portions of enlarged ligamentum flavum 26 are extending intospinal canal 81, potentially exerting compressive forces on the spinalcord (not shown) that resides within spinal canal 81.

As previously discussed, to relieve compressive forces on the spinalcord and hence relieve the associated symptoms of spinal stenosis,portions of ligamentum flavum 26 may be excised. However, topercutaneously excise portions of ligamentum flavum 26 via minimallyinvasive techniques, the innate structure of vertebral column 80 andeach vertebra may present significant imaging challenges. For instance,lateral imaging windows/views of ligamentum flavum 26 substantially inthe direction of the z-axis may be obscured by the various processes ofthe vertebrae (e.g., transverse processes, superior articular processes,inferior articular processes), the laminae of each vertebra, etc.Further, some anterior-posterior (A-P) imaging windows/views ofligamentum flavum 26 substantially in the direction of the x-axis mayalso be obscured by the laminae. In particular, in the A-P radiographicimaging planes substantially in the direction of the x-axis, theposterior edges of parallel laminae overlap and obscure ligamentumflavum 26 and interlaminar space 82, particularly the anterior portionsof ligamentum flavum 26 and interlaminar space 82 closest to spinalcanal 81. However, with an imaging window/view in a plane substantiallyparallel to the X-Y plane, at an angle θ generally in the direction ofarrow 83, and slightly lateral to the spinous process, interlaminarspace 82 and ligamentum flavum 26 may be viewed without significantobstruction from neighboring laminae. In other words, imagingwindows/views generally aligned with arrow 83 (FIG. 6) allow a moredirect view of interlaminar space 82 and ligamentum flavum 26 from theposterior back surface with minimal obstruction by the vertebrae,laminae in particular.

Typically, the long axes of the substantially parallel laminae (e.g.,laminae 16 a, 16,b, 16 c) and interlaminar spaces (e,g, interlaminarspaces 82) are generally oriented between 60 and 75 degrees relative toposterior back surface 85. Thus, preferably the imaging means (e.g.,x-ray beam, fluoroscopy tube, etc.) is positioned generally in thedirection represented by arrow 83, where θ is substantially between 60and 75 degrees relative to the anterior back surface 85. In other words,the imaging means is positioned substantially parallel to the surface ofthe laminae. The resulting imaging window/view, termed “caudal-cranialposterior view” hereinafter, permits a clearer, more direct, lessobstructed view of interlaminar space 82 and ligamentum flavum 26 fromthe general posterior back surface 85. The caudal-cranial posterior viewpermits a relatively clear view of interlaminar space 82 and ligamentumflavum 26 in directions generally along the y-axis and z-axis. However,the caudal-cranial posterior view by itself may not provide a clearimaging window/view of interlaminar space 82 and ligamentum flavum 26 indirections generally along the x-axis. In other words, thecaudal-cranial posterior view by itself may not provide a clear imagingwindow/view that can be used to accurately determine theposterior-anterior depth, measured generally along the x-axis, of adevice across the ligamentum flavum 26.

Thus, in preferred embodiments, an additional imaging window/view,termed “caudal-cranial posterior-lateral view” hereinafter, is employedto provide a clearer, unobstructed view of interlaminar space 82 andligamentum flavum 26 in directions generally along the y-axis andz-axis. The caudal-cranial posterior-lateral view is generated byorienting an imaging means generally at an angle θ relative to outersurface of the patient and also angling such imaging means laterally inan oblique orientation, revealing a partial lateral view of interlaminarspace 82 occupied by ligamentum flavum 26 on the anterior side of thelamina and posterior to the underlying dural sac (not shown) and spinalcord (not shown).

By employing at least one of the caudal-cranial posterior view and thecaudal-cranial posterior-lateral views, relatively clear imagingwindows/views of the interlaminar space 82 and ligamentum flavum 26 indirections along the x-, y-, and z-axes may be achieved.

FIG. 8 illustrates vertebral column 80 and an instrument 101. Onceunobstructed imaging windows/views of interlaminar space 82 andligamentum flavum 26 are established in the manner described above,instrument 101 is employed to percutaneously access interlaminar space82 and ligamentum flavum 26. Instrument 101 may be any suitable devicenecessary to perform the MILD procedures described herein includingwithout limitation a tissue excision device, a cannula employed to guidea tissue excision device, or combinations thereof. Tissue excision toolsand devices are described in more detail below.

More specifically, using images of the interlaminar space 82 andligamentum flavum 26 obtained from the desired direction(s), (e.g.,caudal-cranial posterior view and the caudal-cranial posterior-lateralview), instrument 101 can be employed to penetrate the skin and softtissue in the posterior back surface 85 of the patient In preferredembodiments, the skin entry point for instrument 101 is between 5 and 10cm inferior (caudal to) the posterior surface of the interlaminar space82 of interest For instance, if the portion of ligamentum flavum 26between lamina 16 a and lamina 16 b is the area of interest, theninstrument 101 may be inserted into the patient's back about 5 to 10 cminferior to posterior surface 84 of interlaminar space 82.

Referring now to FIG. 7, instrument 101 is preferably initially insertedinto the posterior tissue and musculature of the patient generallyparallel to the longitudinal axis of spinal column 80. In other words,the angle β between the posterior back surface 85 and instrument 101 isbetween 0 and 10 degrees when instrument 101 is initially inserted.Further, instrument 101 is preferably inserted into the posterior tissueand musculature of the patient on the same side (ipsilateral) of themedian plane as the area of interest (e.g., the targeted portion ofligamentum flavum 26), as best seen in FIG. 4. Once instrument 101 isinserted into the posterior tissue and musculature of the patient,instrument 101 then may be oriented 5 to 90 degrees relative to theposterior back surface 85 in order to create a trajectory acrossligamentum flavum 26 in the area of interest. It is to be understoodthat once instrument 101 is inserted into the patients posterior backsurface 85, the ends of instrument 101 are free to pivot about theinsertion location in posterior back surface 85 in the general directionof the y-axis and the z-axis, and may be advanced posteriorly oranteriorly generally in the direction of the x-axis.

Once inserted into the posterior tissue and musculature of the patient,instrument 101 can be positioned to provide a trajectory acrossinterlaminar space 82 in the area of interest, generally towards theanterior surface of the lamina superior to the area of interest. Forexample, if interlaminar space 82 between lamina 16 a and lamina 16 b isthe area of interest, instrument 101 is positioned to provide atrajectory that will allow a cutting instrument to be inserted acrossinterlaminar space 82 between lamina 16 a and lamina 16 b towards theanterior surface of lamina 16 a (superior lamina).

By switching between the caudal-cranial posterior view and thecaudal-cranial posterior-lateral view, or by viewing both thecaudal-cranial posterior view and the caudal-cranial posterior-lateralview at the same time, instrument 101 can be advanced to ligamentumflavum 26 in the area of interest with more certainty than hasheretofore been present. Once instrument 101 has reached ligamentumflavum 26, portions of ligament flavum 26 may be excised with a tissueexcision device so as to relieve pressure on the spinal nerves. Ifinstrument 101 comprises a tissue excision tool, instrument 101 may beinserted into ligamentum flavum 26 to resect portions of ligamentumflavum 26. However, if instrument 101 comprises a cannula, instrument101 will be positioned adjacent the ligamentum flavum 26 in the regionof interest and a tissue excision device may be advanced throughinstrument 101 toward ligamentum flavum 26 and inserted in ligamentflavum 26 in the region of interest to retract tissue therefrom. In someembodiments, excision can be performed generally from posterior toanterior across interlaminar space 82 and then laterally along theanterior portion of ligament flavum 26 if desired. The actual depth ofthe tip of instrument 101 (or any tissue excision device passing throughinstrument 101 in the case instrument 101 is a cannula) in the generaldirection of the x-axis may be adjusted with guidance from thecaudal-cranial posterior-lateral view and appropriateretraction/advancement of instrument 101 and appropriate adjustment ofinstrument 101 between 5 and 90 degrees relative to the posterior backsurface 85.

Referring to FIG. 4, the tip of an exemplary tissue excision device 100is shown schematically within ligamentum flavum 26. Tissue excisiondevice 100 may be the same device as instrument 101, or may be a toolpassed through instrument 101 if instrument 101 is a cannula. Inparticular, device 100 has accessed ligamentum flavum 26 according tothe ILAMP method previously described. Thus, device 100 is positioned toexcise portions of ligamentum flavum 26 on the same lateral side ofmedian plane 210 as device 100 is percutaneously inserted. In otherwords, in the view shown in FIG. 4, device 100 is inserted into the bodyon the right side of median plane 210 and enters ligamentum flavum 26 onthe right side of median plane 210 to excise portions of ligamentumflavum 26 on the right side of median plane 210. In FIG. 4, device 100does not cross median plane 210.

FIG. 5 illustrates an embodiment of an alternative MILD method in whichexemplary tissue excision device 100 is positioned to excise portions ofligamentum flavum 26 on the opposite lateral side of median plane 210 asdevice 100 is percutaneously inserted. More specifically, device 100 isinserted into the body on the rights side of median plane 210, entersligamentum flavum 26 on the right side of median plane 210, but ispositioned to excise portions of ligamentum flavum 26 on the left sideof median plane 210. In FIG. 5, device 100 crosses median plane 210.

In the manner described, portions of the ligamentum flavum can beexcised by a percutaneous MILD procedure. In particular, with theapproach described and as best illustrated in FIGS. 4 and 6, ligamentumflavum 26 can be accessed, and portions thereof removed via theinterlaminar space on the same lateral side (ipsilateral) of medianplane 210 as the entry point for instrument 101 (e.g., a cannula, atissue excision tool, etc.). This approach may sometimes hereinafter bereferred to as an Iplsilateral Approach MILD Procedure (ILAMP).

Tissue Excision Devices

Embodiments of tissue excision tools, devices, and methods disclosedherein may take several forms and may be used according to the ILAMPmethod described above, or used according to alternative MILD procedures(e.g., MILD procedure schematically illustrated in FIG. 5). One suchalternative MILD procedure is disclosed in U.S. application Ser. No.11/193,581, which is hereby incorporated herein by reference in itsentirety. In the descriptions of the tissue excision devices below, thedistal portions of the devices are described in detail. As used herein,the term “distal” refers to positions that are relatively closer to theregion of interest (e.g., the thickened portion of the ligamentum flavumto be decompressed). An exemplary embodiment of a proximal end for thetissue excision devices, including an actuation means, is also describedbelow. However, it is to be understood that embodiments of tissueextraction devices described herein may be used with a variety ofproximal ends and a variety of actuation means that are known andunderstood by those skilled in the art.

FIGS. 9 and 10 illustrate the distal portion of an embodiment of atissue excision device 200 in an opened position. Tissue excision device200 comprises an inner tubular member 230 coaxially disposed within andslidingly engaging an outer tubular member 210. Inner and outer tubularmembers 230, 210 share a central longitudinal axis 250. Outer member 210has an inner radius R₁, as measured from axis 250, and inner member 230has an outer radius R₂, as measured from axis 250. In this embodiment,outer radius R₂ is substantially the same or slightly less than innerradius R₁ such that the outer surface of inner tubular 230 slidinglyengages the inner surface of tubular 210. Thus, outer tubular 210 andinner tubular 230 are permitted to move axially (i.e., along axis 250)relative to each other. Tubulars 210, 230 may be formed from anysuitable hollow bodies including without limitation a hypotube, cannula,or catheter. Although tubulars 210, 230 shown in FIGS. 9 and 10generally have a circular cross-section, in general, members 210, 230may have any suitable shape and cross-section including withoutlimitation circular, oval, or rectangular.

Inner tubular 230 includes a central through bore 240 and a distal end260. Bore 240 runs the length of inner tubular 230 and provides a voidor space that may be filled with tissue excised by device 200 (e.g.,excised pieces of ligamentum flavum). Distal end 260 includes an uppermember 231 and a lower member 232. Distal end 260, including uppermember 231 and lower member 232, completely extends from outer tubular210 when device 200 is in the opened position as illustrated in FIGS. 9and 10. Upper member 231 and lower member 232 are preferably integralwith and formed from inner tubular 230. In such embodiments, distal end260 of inner tubular 230 may be formed into an upper member 231 andlower member 232 by any suitable means including without limitationcasting or molding, laser cuffing, machining, hot or cold working, orcombinations thereof.

Lower member 232 preferably comprises a fixed end 232 a integral withinner tubular 230 and a cutting end 232 b, including a cutting tip 234,that cuts through tissue as lower member 232 is advanced through tissue.Cutting tip 234 preferably has a sharpened or beveled edge defined by anacute angle λ that is preferably between 15° and 45°. In the embodimentillustrated in FIGS. 9 and 10, lower member 232 is an extension of innertubular 230 and thus is coaxial with outer tubular 210. As previouslymentioned, lower member 232 is preferably integral with inner tubular230. However, it should be understood that lower member 232 mayalternatively be a distinct component that is mechanically coupled toinner tubular 230 at fixed end 232 a. In such alternative embodiments,lower member 232 may be coupled to inner tubular 230 by any suitablemeans including without limitation welding, pins, or combinationsthereof. In addition, lower member 232 is preferably a relatively rigidstructure that experiences minimal flexing and bending as it is advancedthrough tissue. Further, it should be appreciated that in the embodimentillustrated in FIGS. 9 and 10, no portion of lower member 232 is locatedat a radial distance (as measured perpendicularly from axis 250) greaterthan inner radius R₁ of outer tubular 210, even when device 200 is inthe opened position.

Referring still to FIGS. 9 and 10, upper member 231 includes a fixed end231 a integral with inner tubular 230 and a cutting end 231 b, includinga cutting tip 233, that cuts through tissue as upper member 231 isadvanced through tissue. Cutting tip 233 preferably has a sharpened orbeveled edge defined by an acute angle α that is preferably between 20°and 45°.

In addition, upper member 231 is disposed at an angle θ with respect tolower member 232. When device 200 is in the fully opened positionillustrated in FIGS. 9 and 10, angle θ is at a maximum, termed hereinopen angle θ_(O). In general, the angular separation of upper member 231and lower member 232 results from the bending or flexing of upper member231 in a resilient flexing region 235 near fixed end 231 a.Specifically, when upper member 231 is manufactured, upper member 231 isshaped or plastically deformed at flexing region 235 so as to form openangle θ_(O). For an upper member 231 having a length between 0.5″ and1.0″ (as measured from cutting tip 233 to fixed end 231 a), open angleθ_(O) is preferably between 5° and 30°, and more preferably between 8°and 20°.

Although flexing region 235 defines the opened position of upper member231, upper member 231 may be elastically flexed within or about flexingregion 235. Thus, upper member 231 may be described as being biased tothe opened position, i.e. upper member 231 tends to return to open angleθ_(O) whenever it is flexed to an angle θ that differs from open angleθ_(O).

As previously described, flexing region 235 is formed by plasticallydeforming, bending, or otherwise shaping upper member into the openedposition shown in FIGS. 9 and 10. In alternative embodiments, uppermember 231 may be a distinct component that is mechanically connected toinner tubular 230. In such alternative embodiments, flexing region 235may be formed by a pivotal connection between upper member 231 and innertubular 230 that is biased opened, such as by a spring or the like.Thus, although upper member 231 elastically bends or flexes at flexingregion 235 in the embodiments described herein, flexing region 235 mayalso be described as a pivoting region.

Referring still to FIGS. 9 and 10, upper member 231 extends inward(toward axis 250) at a second angled or bent region 237, forming a tooth239 near cutting end 231 b. The amount or degree of bending at angledregion 237 is defined by an angle ρ relative to axis 250. Angled region237 preferably has an angle ρ between 10° and 30°, and more preferablybetween 12° and 25°. Further, angled region 237 preferably has asmoothly contoured outer surface to enhance the ability of distal end260 to pass smoothly through tissue. In addition to its utility inexcising tissue, the inclusion of angled region 237 extending radiallybeyond outer radius R₃ of outer tubular 210 offers the potential forimproved fluoroscopic visualization, and hence control, of distal end260 of device 200. For instance, under fluoroscopic visualization,angled region 237 may project beyond any shadowing generated by otherportions of device 200, such as a handle attached to device 200, etc.

As best seen in FIG. 9, upper member 231 is preferably slightly longerthan lower member 232. Thus, as upper member 231 and lower member 232are preferably sized and shaped such that upper member 231 can “clampdown” and mate with lower member 232 when upper member 231 flexes aboutflexing region 235 toward lower member 232 in the direction of arrow238. Specifically, as upper member 231 flexes toward lower member 232,tooth 239 moves toward and preferably ultimately engages free end 232 band cutting tip 234 of lower member 232. It is to be understood that asupper member 231 pivots or flexes about flexing region 235 in thedirection of arrow 238, the angle θ between upper member 231 and lowermember 232 decreases.

FIGS. 11-13 schematically illustrate the transition of tissue excisiondevice 200 from the opened position (FIG. 11) to the closed position(FIG. 13). As shown in FIG. 11, tissue excision device 200 fully open.When device 200 is in the opened position, distal end 260 of innertubular 230 is fully extended from outer tubular 210 and upper member231 is biased away from lower member 232 and disposed at open angleθ_(O) relative to lower member 232. To close tissue excision device 200,outer tubular 210 is advanced toward distal end 260 generally in thedirection of arrow 270. As outer tubular 210 advances over distal end260, the inner surface of outer tubular 210 engages the outer surface ofupper and lower members 231, 232, In particular, the inner surface ofouter tubular 210 engages the portions of upper member 231 that extendradially beyond the inner radius R₂ of outer tubular 210. As a result,the inner surface of outer tubular 210 exerts a force on the outersurface of upper member 231, causing upper member 231 to elasticallyflex or pivot about flexing region 235 in the direction of arrow 238.Consequently, the angle θ decreases, as best seen in FIG. 12. As outertubular 210 is advanced over distal end 260, upper member 231 continuesmove toward lower member 232. In FIG. 13, tissue excision device 200 hasachieved a fully closed position. When device 200 is in the fully closedposition, upper member 231 and lower member 232 are completely disposedwithin outer tubular 210 and angle θ between upper member 231 and lowermember 232 is at a minimum, termed herein closed angle θ_(C). Inparticular, when device 200 is in the fully closed position, closedangle θ_(C) between upper member and lower member is preferably between0° and 5°.

Referring briefly to FIG. 16, another embodiment of a tissue excisiondevice 400 is schematically illustrated. Like device 200, tissueexcision device 400 comprises an inner tubular member 430 coaxiallydisposed within an outer tubular member 410. Inner tubular 430 includesa distal end 460 having an upper member 431 and a lower member 432.Upper member 431 includes a cutting tip 433 and lower member 432includes a cutting tip 434. Device 400 operates substantially the sameas device 200, with the exception that device 400 includes two movablemembers 431, 432 that each operate similarly to upper member 231 ofdevice 200. When device 400 is in the opened position illustrated inFIG. 16, both upper member 331 and lower member 332 extend radiallybeyond the inner radius of outer tubular 410 (as measured from axis450). When device 400 is actuated into the closed position, upper member431 and lower member 432 are urged toward each other as outer tubular410 advances over distal end 460.

Tissue Excision and Removal

FIGS. 14 and 15 schematically illustrate the excision of a portion oftissue 126 by device 200. In some embodiments, a portal or cannula (notshown) may be employed to provide percutaneous access to tissue 126. Forinstance, tissue excision device 200 may be inserted into and advancedthrough such a portal or cannula to reach tissue 126. U.S. applicationSer. No. 11/461,020 filed concurrently herewith, which is herebyincorporated herein by reference in its entirety, discloses severaltools, devices and methods for employing a portal to providepercutaneous access to a tissue of interest. If a portal or cannula isused to guide device 200, device 200 may be passed through such cannulain the opened position or closed position.

Regardless of the manner in which tissue excision device 200 reaches thetissue of interest (e.g., by portal or otherwise), prior to insertioninto the tissue to be excised, device 200 is configured in the openedposition as shown in FIGS. 9, 11, and 14. With device 200 in the openedposition, the distal portion of tissue excision device 200 is advancedinto tissue 126, as best shown in FIG. 14. Tissue 126 may be any type oftissue to be excised and removed from a patient including withoutlimitation, soft tissue, fat, muscle, or bone. When used to treat spinalstenosis caused by a thickened ligamentum flavum, distal end 260 ofdevice 200 is preferably inserted into the stenotic ligamentum flavum26, preferably posterior to a safety zone 40, in order to safely cut andremove portions of the thickened ligamentum flavum 26 (see FIGS. 2 and3), thereby reducing the stenosis.

Still referring to FIGS. 13 and 14, as device 200 is inserted andadvanced into tissue 126, cutting tips 233, 234 cut through tissue 126.In addition, as device 200 is advanced into tissue 126, portions oftissue 126 cut by cutting tips 233, 234 slide into and fill at least aportion of bore 240 of inner tubular 230. It is to be understood thatthe farther device 200 is advanced into tissue 126, the more tissue 126is cut, and the greater the amount of cut tissue 126 that will occupyinner bore 240 Upper member 231, including flexing region 235 and angledregion 237, as well as lower member 232 are preferably sufficientlyrigid that the device does not inadvertently transition to the closedposition as device 200 is advanced through the tissue. In other words,upper member 231 and lower member 232 are preferably sufficiently rigidand are configured such that the forces exerted on the outer surface ofupper member 231 and lower member 232 by the surrounding tissue 126 asdevice 200 is advanced does not tend to move upper member 231 towardslower member 232.

In some embodiments, distal end 260 is shaped and configured such thatthe forces exerted on the inner surfaces of distal end 260 by tissueentering bore 240 are substantially balanced by the forces acting on theoutside surfaces of distal end 260. In other embodiments, the distanceperpendicular to axis 250 between cutting tip 233 and cutting tip 234 is80% to 120% of the diameter of bore 240.

Once the desired amount of tissue has been cut by device 200 anddisposed within inner bore 240, outer tubular 210 may be slid toward andover distal end 260, thereby closing device 200 as previously described.As upper member 231 and lower member 232 move towards each other, tissue126 within bore 240 is severed from the surrounding tissue 126. Forinstance, tooth 239 and cutting tip 233 slice tissue extending axiallyfrom bore 240, and annular cutting edge 211 of outer tubular 210 slicestissue extending radially from bore 240 between upper member 231 andlower member 232. In some embodiments, cutting edge 211 of outer tubular210 is sharpened or beveled to enhance the cutting ability of outertubular 210. Once device 200 has achieved the closed position, device200 may be retracted from tissue 126 as best shown in FIG. 15. Theportion of tissue 126 contained within inner bore 240 is removed alongwith device 200. Once device 200, including a portion of tissue 126within inner bore 240, has been completely removed from the patient,resected tissue within bore 240 is removed from bore 240 (i.e., bore 240is emptied) so that device 200 may be reinserted into tissue 126 tocontinue to the cutting and removal of portions of tissue 126.

Pieces of tissue 126 captured within inner bore 240 may be removed bysimply opening device 200 and pulling the pieces of tissue from innerbore 240. Device 200 may be opened from the closed position byretracting outer tubular 210 from inner tubular 230, thereby extendingdistal end 260 from outer tubular 210. As device 200 transitions to itsopened position, upper member 231 and lower member 232 will separate andangle θ will increase, allowing the user to access inner bore 240. Inpreferred embodiment, once outer tubular 210 is sufficiently retracted,upper member 231 will retake its initial open position with angle η andangle θ at their respective maximums. In other words, upper member 231is sufficiently rigid to rebound to its original opened position onceouter member 210 no longer restricts the radial movement of upper member231 (i.e., upper member 231 acts like a spring).

In an alternative embodiment, a plunger or tissue ejector may beincluded with device 200, 300 to physically eject the excised tissue 126from inner bore 240. For instance, a plunger 372 (FIG. 10) may beincluded within device 200 to push cut tissue within inner bore 240 outthrough the openings in distal end 260. Such embodiments are describedin more detail below.

The process of inserting device 200 into tissue 126 in the openedposition, closing device 126, retracting device 200 in the closedposition, opening device 200, emptying inner bore 240, and reinsertingdevice 200 may be repeated until the desired amount of tissue 126 hasbeen excised and removed. Referring briefly to FIG. 3, when device 200is employed to remove portions of thickened ligamentum flavum 26, thisprocess may be repeated until the spinal canal is adequatelydecompressed. Further, when device 200 is employed to remove portions ofthickened ligamentum flavum 26, the tips 233, 234 of device 200 arepreferably controlled to remain within ligamentum flavum 26 and notpenetrate safety zone 40. Nonetheless, safety zone 40 is preferablyprovided so that even an inadvertent penetration into epidural space 27by device 200 will not result in damage to the dural sac 32 or nerves34.

The components of tissue excision device 200 (e g., outer tubular 210,inner tubular 230, members 231, 233, etc.) may comprise any suitablematerial(s) including without limitation metals (e.g., stainless steel,titanium, etc.), non-metals (e.g., polymer, composites, etc.) orcombinations thereof. The components of tissue excision device 200 arepreferably manufactured from a durable biocompatible material such astitanium or stainless steel, but may alternatively be polymeric. Inaddition, members 231, 233 each preferably comprise a relatively rigidmaterial(s) capable of maintaining their shape and configuration wheninserted into and advanced through tissue. Further, upper member 231preferably comprises a resilient material having the ability to berepeatedly flexed from its initial opened position to its closedposition (e.g., by pivoting about flexing region 235) and vice versawithout cracking or otherwise being damaged. Similarly, it is desirablethat upper member 231 resume its initial opened position when device 200is transitioned from closed to opened (e.g., as outer tubular 210 isretracted from distal end 260, thereby allowing distal end 260 to extendfrom outer tubular 210). Thus, it is also preferred that upper member231 comprise a resilient material capable resuming its originalconfiguration once external forces (e.g., force applied by outer tubular210) are removed.

In addition, the components of tissue excision device 200 may bemanufactured by any suitable methods. Examples of suitable methodsinclude casting or molding, machining, laser cutting, EMD, orcombinations thereof. In some embodiments, cutting edges or tips may beelectro polished to for sharpening. The components of tissue excisiondevice 200 may be assembled by any suitable method including withoutlimitation welding, press fitting, or combinations thereof. Stillfurther, the inner surface of inner tubular 230 may be roughened byknurling, sand blasting, bead blasting, plasma etching, or othersuitable means to enhance the ability of inner bore 240 to enhancegrasping and retention of excised portions of tissue.

Multi-Function Tool for Tissue Ejection

Referring now to FIG. 17, the invention further includes amulti-function tool 300 that provides both tissue-resection and sampleclearance. In certain embodiments, the multi-function tool supportsone-handed operation, thereby increasing usability by the physician.Tool 300 generally includes a housing 310 having a bore 320 therethroughand a guide tube 330, trigger 350, and plunger 370 reciprocably disposedin bore 320. Housing 310 includes a body 312 with a grip 314 extendingtherefrom. Grip 314 is preferably ergonomically sized and shaped so thatit can be easily and firmly grasped by a physician. Body 312 has aproximal end 315 and a distal end 317.

A trigger chamber 318 is disposed within body 312 and includes a triggeropening 319 adjacent to grip 314. Bore 320 preferably extends throughhousing 310 from proximal end 315 to distal end 317, intersectingtrigger chamber 318. Bore 320 preferably includes a reduced diameterportion 324, which extends from distal end 317 to trigger chamber 318,and a larger diameter portion 326, which extends from trigger chamber318 to proximal end 315.

Guide tube 330 is slidably received in bore 320. In some embodiments,guide tube 330 may be the same component as outer tubular 210 describedabove with regard to tissue excision device 200 (FIG. 10). Guide tube330 is preferably sized so that its outer diameter is slightly less thanthe inside diameter of reduced diameter bore portion 324. Guide tube 330has a proximal end 335 and a distal end 337. A sleeve 332 is preferablyaffixed to guide tube 330 at or near proximal end 335. Sleeve 332preferably includes a trigger-engaging means 333 for engaging trigger350, as described in detail below.

Disposed within guide tube 330 is a tissue-engaging means such as atissue clamp 340. Tissue clamp 340 may be a rod 342 having a proximalend 345 and a distal end 347. In some embodiments, the distal end 347may include a tissue excision device (e.g., tissue excision device 200)as described elsewhere herein. The proximal end 345 of tissue clamp 340may include a stop 344 or other means for preventing movement of tissueengaging means 340 relative to body 312. Stop 244 may be rigidly affixedto tissue clamp 340 and may be held in place within body 312 by a pin245. In alternative embodiments, proximal end 345 is held in placewithin body 312 by welding, pinning, crimping, or any other suitablemeans.

Trigger 350 has an inner end 355 and an outer end 357. Outer end 357preferably includes a finger ring 352 or other similar ergonomicconfiguration that allows outer end 357 to be easily manually actuatedtoward grip 314. The inner end 355 of trigger 350 preferably includes atleast one arm 358, which extends adjacent to and beyond guide tube 330.In preferred embodiments, arm 358 slidably engages trigger-engagingmember 333 on guide tube 330. Trigger 350 is preferably pivotallymounted to housing 310 at a pivot point 359 between its inner and outerends 355, 357. In certain embodiments, pivot point 358 is closer toinner end 355 than it is to outer end 357, so that a mechanicaladvantage can be employed during operation of the tool. A rotation stop360 is preferably provided within cavity 318 and positioned so that itprevents rotation of inner trigger end 355 beyond a certain point.

In certain embodiments, tissue clamp 340 is provided as a hollow tube orrod. In these embodiments, it is preferred to provide a tissue ejectionsystem 370. Tissue ejection system 370 may comprise yet another rod ortube 372 (also shown in phantom in FIG. 10), which is coaxial with andslidably disposed within tissue clamp 340. Rod 372 is initiallypositioned so that it extends out of the proximal end of tissue clamp340 and its distal end 373 is disposed within tissue clamp 340 at apoint that is slightly inward of the tissue resection means. Tissueejection system 370 may include a plunger head 380 affixed to theproximal end of rod 372. Plunger head 380 preferably includes a plungerbody 382 having distal and proximal ends 385, 387, respectively, and aknob or button 384 affixed to proximal end 387 of plunger body 382. Aspring 374 or other biasing means is preferably mounted between thedistal end 385 of plunger body 382 and stop 244.

In some embodiments, the outer surface of plunger body 382 preferablyincludes an offset portion 386 defined at its ends by distal andproximal shoulders 387, 388, respectively. A pin 389 is provided in body312 and positioned so that it engages offset portion 386. While rod 372is slidably within body 312, its axial movement in the distal directionis limited by engagement of pin 389 with proximal shoulder 388 and inthe proximal direction by distal shoulder 387. Spring 274 is preferablyconfigured such that it is slightly compressed when pin 389 engagesdistal shoulder 387. Thus, plunger head 380 is normally urged in theproximal direction so that it extends beyond the proximal end 315 of thedevice.

Operation of Multi-Function Tool

In operation, when it is desired to resect tissue from within a patient,the present multi-function tool allows a surgeon to remove a desiredamount of tissue efficiently and precisely. In many instances, thetissue that is to be resected lies beneath the skin, and possibly withinor adjacent to bone. For example, when stenosis is caused by hypertrophyof the ligamentum flavum, it may be desirable to remove portions of thehypertrophied ligament. In such cases, access to the resection site maybe provided by inserting a trocar and cannula (e.g., instrument 101 inFIG. 8) through the skin and intervening soft tissue as describedelsewhere herein. Once the tip of the device has reached the resectionsite, the trocar can be removed, leaving the cannula in place to serveas a portal to the site. In the case of a hypertrophied ligamentumflavum or other stenosis, it may be preferred to use an ipsilateraltechnique, as described elsewhere herein.

With the cannula in place, or not, the distal end of the present tool300 is inserted to the resection site as shown in FIG. 18. Depending onthe inner diameter of the cannula, the tissue excision device on the endof tool 300 may or may not be open as it passes through the cannula.Because the distal end 347 of tissue clamp 340 includes a tissueexcision device (e.g., device 200 shown in FIG. 9) it will tend toengage, or “bite into” tissue as it advances out of the end of thecannula. When a desired amount of tissue has been engaged, up to thecapacity of the excision device, that tissue can be resected byadvancing guide tube 330 axially toward the distal end 347. As itadvances, guide tube 330 bears on the outer surface of the tissueexcision device (e.g., outer surface of upper member 231 shown in FIG.10), urging the tissue excision device into a closed position. As thetissue excision device reaches the closed position, a segment of tissueis resected and retained within the tissue excision device (e.g., withinbore 240 shown in FIG. 10). Guide tube 330 is advanced by applyingpressure in the proximal direction on the outer end 357 of trigger 350.This causes trigger 350 to pivot around point 359, which in turn causesarm 358 to urge sleeve 332 in the distal direction. As sleeve 332 andtube 330 move in the distal direction, arm 358 pivots and shiftsrelative to sleeve 332. As the distal end 337 of the guide tube reachesthe distal end 347 of the tissue clamp, it is prevented from advancingfurther by engagement with stop 360.

The closed tool 300, containing the segment of resected tissue, may thenbe pulled back, out of the cannula and emptied. To empty the tool 300,trigger 350 is urged distally, thereby causing guide tube 330 to retractinto tool 300, which in turn allows the tissue excision device to open.Because it is not uncommon for the tissue segment to remain stuck withinthe device, tissue ejection system 370 may be used to discharge thetissue segment. Tissue ejection system 370 is actuated by applyingpressure to knob 384, urging it in the distal direction. As it advances,plunger body 382 advances within the bore or lumen of the tissueexcision device (e.g., bore 240 shown in FIG. 10), compressing spring374. The distal end 373 of the plunger advances, pushing the tissuesegment out as it does so. Once the tissue segment has been ejected,removing pressure from know 384 will allow spring 374 to return theplunger to its normal position, advancing rod 372 in the proximaldirection until distal shoulder 387 bears on pin 380.

With the completion of these steps, tool 300 is ready to resect anothertissue segment. It will be understood that the steps can be carried outin different sequences, depending on the desired objective. For example,tool 300 can be advanced to the desired resection site in a closedposition, rather than an open position.

The ILAMP methods and techniques described herein allow spinaldecompression to be performed percutaneously, avoiding the pain, lengthyrecovery time, and risk associated with open surgery. In addition, theILAMP methods and techniques described herein permit clearer, lessobstructed imaging views of the interlaminar spaces and ligamentumflavum between the laminae in the areas of interest. Such improvedimaging views offer the potential for enhanced accuracy and safety inthe placement of tools within the ligamentum flavum proximal theepidural space and spinal cord. Further, the excision tools and devicesdescribed herein may be employed with the ILAMP methods, or alternativepercutaneous methods, to excise portions of a thickened ligamentumflavum, thereby reducing spinal stenosis caused by such enlargedligamentum flavum.

Through the provision of a safety zone and improved imaging, the presentdevices and techniques offer reduced risk of spinal cord damage. Inaddition to improving nerve function, it is expected that decompressionof the spinal canal in the manner described herein will result inimproved blood flow to the neural elements by reducing the extrinsicpressure on the spinal vasculature. For these reasons, it is believedthat spinal decompression performed according to embodiments of thepresent invention will be preferable to decompression operationsperformed using currently known techniques.

While preferred embodiments of this invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the scope or teaching of this invention. Forexample, the means by which the safety zone is formed may be varied, theshape and configuration of the tissue excision devices may be varied,and the steps used in carrying out the technique may be modified.Accordingly, the invention is not limited to the embodiments describedherein, but is only limited by the claims that follow, the scope ofwhich shall include all equivalents of the subject matter of the claims.Likewise, the sequential recitation of steps in a claim, unlessexplicitly so stated, is not intended to require that the steps beperformed in any particular order or that a particular step be completedbefore commencement of another step.

1-19. (canceled)
 20. A medical device, comprising: a guide tube having aproximal end, a distal end, and a lumen extending from the proximal endto the distal end along a longitudinal axis of the guide tube, whereinthe distal end includes an aperture having an elliptical shape angledfrom about 30 degrees to about 60 degrees relative to the longitudinalaxis; and a tissue clamp having a distal region and a proximal region,wherein the proximal region is slidingly received in the lumen and thedistal region has an upper member rotationally coupled to a lowermember, the upper member including a distal tip having a sharp edgeangled towards the longitudinal axis and the lower member including adistal tip having a sharp edge angled parallel to the longitudinal axis;and wherein, when the distal region is generally located outside of thelumen, the upper member is angled away from the longitudinal axis andthe sharp edges of the upper and lower members are both positioned to atleast partially cut tissue when the tissue clamp is moved along thelongitudinal axis; and wherein, when the distal region is generallylocated within the lumen, the upper member is positioned generallyparallel to the longitudinal axis and the sharp edges of the upper andlower members engage to generally close the aperture of the guide tube.21. The medical device of claim 20, wherein the sharp edges of the upperand lower members are generally U shaped.
 22. The medical device ofclaim 20, wherein the lower member is positioned parallel to thelongitudinal axis when the distal region is generally located outside ofthe lumen.
 23. (canceled)
 24. (canceled)
 25. The medical device of claim20, wherein the tissue clamp is configured to receive a rod to move atissue sample located within the tissue clamp.
 26. A medical device,comprising: a guide tube having a proximal end, a distal end, and alumen extending from the proximal end to the distal end along alongitudinal axis of the guide tube, wherein the distal end includes anaperture having an elliptical shape positioned at an angle relative tothe longitudinal axis; and a tissue clamp having a distal region andproximal region, wherein the proximal region is slidingly received inthe lumen and the distal region has an upper member moveably coupled toa lower member, the upper member including a distal tip angled towardsthe longitudinal axis and the lower member including a distal tip angledparallel to the longitudinal axis; and wherein, when the distal regionis generally located outside of the lumen, the upper member is angled,away from the longitudinal axis and the upper and lower members are bothconfigured to cut tissue when the tissue clamp is moved along thelongitudinal axis; and wherein, when the distal region is generallylocated within the lumen, the upper member is positioned generallyparallel to the longitudinal axis and a curved outer surface of a distalpart of the upper member is substantially parallel to the angle of theaperture of the guide tube.
 27. The medical device of claim 26, whereinan area of the curved outer surface is substantially similar to an areaof the elliptical shape of the aperture of the guide tube such that thecurved outer surface generally fills the aperture when the distal regionis generally located within the lumen.
 28. The medical device of claim26, wherein at least part of the curved outer surface extends beyond theaperture of the guide tube to form a blunt distal end of the tissueclam, when the distal region is generally located within the lumen. 29.A medical device, comprising: a guide tube having a longitudinal axis, adistal aperture, a proximal end, and a lumen extending from the distalaperture of the guide tube towards the proximal end of the guide tube,wherein the distal aperture is angled relative to the longitudinal axisto form a leading edge and a trailing edge about a periphery of thedistal aperture, and the leading edge located distal to the trailingedge; and a tissue clamp formed from a tube having a distal end and aproximal end, wherein the tissue clamp is at least partially disposedwithin the lumen and is moveable along the longitudinal axis relative tothe guide tube, the distal end of the tissue clamp including an uppermember and a lower member, the upper member having a first bend regionin a proximal end of the upper member, a second bend region in a distalend of the upper member, and a medial region located between the firstbend region and the second bend region, and wherein the first bendregion is flexible and concave to bend an outer surface extending alongthe upper member away from the longitudinal axis about the first bendregion, the second bend region is rigid and convex to bend the outersurface of the upper member towards the longitudinal axis about thesecond bend region, and the trailing edge of the distal aperture isconfigured to engage the upper member of the tissue clamp to move theupper member towards the lower member.
 30. The medical device of claim29, wherein the lower member is angled parallel to the longitudinalaxis.
 31. The medical device of claim 30, wherein the upper memberincludes a distal tip having a sharp edge angled towards thelongitudinal axis and the lower member includes a distal tip having asharp edge angled parallel to the longitudinal axis.
 32. (canceled) 33.The medical device of claim 31, wherein the trailing edge of the distalaperture is configured to engage the outer surface of the medial regionto move the distal tip of the upper member towards the distal tip of thelower member.
 34. The medical device of claim 33, wherein the trailingedge of the distal aperture is configured to engage the second bendregion to substantially close the distal aperture with the distal end ofthe upper member.
 35. The medical device of claim 34, wherein the sharpedge of the upper member is configured to engage the sharp edge of thelower member when the trailing edge of the distal aperture engages thesecond bend region of the upper member and the leading edge of thedistal aperture engages the lower member.
 36. A medical device,comprising: a guide tube comprising a hollow, rigid, metal tube having alumen extending along a longitudinal axis of the guide tube; and atissue clamp comprising a metal tube having a distal region and aproximal region, wherein the distal region includes an upper jaw memberand a lower jaw member, the lower jaw member being rigid and extendingparallel to the longitudinal axis, the upper jaw member being flexibleand configured to close relative to the lower jaw member to at leastpartially cut tissue, and at least part of the proximal region isslidingly received in at least part of the lumen of the guide tube; andwherein, when the distal region is generally located outside of thelumen, the upper member is angled away from the lower member and a sharpedge of the upper members is angled towards the lower member to cuttissue when the tissue clamp is moved along the longitudinal axis; andwherein, when the distal region is generally located within the lumen,the upper member is angled generally parallel to the lower member togenerally close a distal opening of the lumen.
 37. The medical device ofclaim 36, wherein the upper member has a first bend region in a proximalend of the upper member and a second bend region in a distal end of theupper member, wherein the first bend region is flexible and concave tobend an outer surface extending along the entire length of the outsideof the upper member away from the lower member about the first bendregion and the second bend region is rigid and convex to bend the outersurface of the upper member towards the lower member about the secondbend region.
 38. The medical device of claim 37, wherein the uppermember further includes an inner surface extending along the entirelength of the inside of the upper member, and the second bend region isconcave to bend the inner surface towards the lower member about thesecond bend region.
 39. The medical device of claim 37, wherein thetissue clamp, when the distal region is generally located within thelumen, includes an inner volume configured to receive a tissue sample,the inner volume extending from the second bend region to at least thefirst bend region.
 40. The medical device of claim 39, further includinga rod located within a lumen of the tissue clamp and configured to movethe tissue sample distally to extract the tissue sample from the tissueclamp when the distal region is generally located outside of the lumen.41. The medical device of claim 20, further including a sharp edgelocated about a periphery of the elliptical shape.
 42. The medicaldevice of claim 20, wherein the tissue clamp includes a generallycylindrical volume configured to receive a tissue sample when the distalregion is generally located within the lumen.
 43. The medical device ofclaim 20, wherein, when the distal region is generally located withinthe lumen, the upper and lower members engage to form a blunt distal endof the tissue clamp that at least partially extends distally beyond theaperture of the guide tube.
 44. The medical device of claim 21, whereinthe sharp edges of the upper and lower members are beveled at an angleranging from about 15 degrees to about 45 degrees relative to thelongitudinal axis.
 45. The medical device of claim 26, wherein the angleof the aperture ranges from about 30 degrees to about 60 degreesrelative to the longitudinal axis.
 46. The medical device of claim 29,wherein the medial region is generally linear along the outer surface ofthe upper member about the medial region.
 47. The medical device ofclaim 29, wherein the distal aperture has an angle of about 45 degreesrelative to the longitudinal axis.
 48. The medical device of claim 47,wherein the periphery of the distal aperture includes a beveled edge.49. The medical device of claim 31, wherein at least one of the distaltip of the upper member and the distal tip of the lower member isgenerally U shaped.
 50. The medical device of claim 49, wherein at leastone of the sharp edge of the upper member and the sharp edge of thelower member is generally U shaped.
 51. The medical device of claim 39,wherein the inner volume is generally cylindrical.